Check out the related section in the new documentation

Advanced interactions with Keymetrics

PMX is a module that allows you to create advanced interactions with Keymetrics. It can be used both on raw Node.js applications and modules.

It allows you to:

  • Expose Functions remotely triggerable from Keymetrics
  • Expose Metrics displayed in realtime and tracked over the time
  • Report Alerts like exceptions or critical issues
  • Report Events to inform about anything
  • Monitor network traffic at the application level and display used ports
  • Analyze HTTP latency

Github repository


Install PMX and add it to your package.json with:

$ npm install pmx --save
var pmx = require('pmx').init({
  http          : true, // HTTP routes logging (default: true)
  ignore_routes : [/socket\.io/, /notFound/], // Ignore http routes with this pattern (Default: [])
  errors        : true, // Exceptions loggin (default: true)
  custom_probes : true, // Auto expose JS Loop Latency and HTTP req/s as custom metrics
  network       : true, // Network monitoring at the application level
  ports         : true  // Shows which ports your app is listening on (default: false)
  alert_enabled : true  // Enable alert sub field in custom metrics   (default: false)

Expose Functions: Trigger Functions remotely

Remotely trigger functions directly from Keymetrics. These features can be found in the main Keymetrics Dashboard page under the Custom Action section.

Simple actions

A simple action allows to trigger a function from Keymetrics. The action command takes a function as a parameter (reply here) and needs to be called once the job is finished.


var pmx = require('pmx');

pmx.action('db:clean', function(reply) {
  clean.db(function() {
     * reply() must be called at the end of the action
     reply({success : true});

Scoped actions

Scoped Actions are advanced remote actions that can also be triggered from Keymetrics.

Two arguments are passed to the function, data (optionnal data sent from Keymetrics) and res that allows to emit log data and to end the scoped action.


pmx.scopedAction('long running lsof', function(data, res) {
  var child = spawn('lsof', []);

  child.stdout.on('data', function(chunk) {
    chunk.toString().split('\n').forEach(function(line) {
      res.send(line); // This sends log to Keymetrics to be saved (for tracking)

  child.stdout.on('end', function(chunk) {
    res.end('end'); // This ends the scoped action

  child.on('error', function(e) {
    res.error(e);  // This reports an error to Keymetrics


Expose Metrics: Measure anything

Keymetrics allows you to expose any metrics from you code to the Keymetrics Dashboard, in realtime. These metrics are located in the main Keymetrics Dashboard page under the Custom Metrics section.

4 helpers are available:

  • Simple metrics: Values that can be read instantly
    • eg. Monitor variable value
  • Counter: Things that increment or decrement
    • eg. Downloads being processed, users connected
  • Meter: Things that are measured as events / interval
    • eg. Requests per minute for a http server
  • Histogram: Keeps a resevoir of statistically relevant values biased towards the last 5 minutes to explore their distribution
    • eg. Monitor the average time of execution of a query into database

Metric: Simple value reporting

This allows to expose values that can be read instantly.

var probe = pmx.probe();

// Here the value function will be called each second to get the value
var metric = probe.metric({
  name    : 'Realtime user',
  value   : function() {
    return Object.keys(users).length;

// Here we are going to call valvar.set() to set the new value
var valvar = probe.metric({
  name    : 'Realtime Value'


Counter: Sequential value change

Things that increment or decrement.

var probe = pmx.probe();

// The counter will start at 0
var counter = probe.counter({
  name : 'Current req processed'

http.createServer(function(req, res) {
  // Increment the counter, counter will eq 1;
  req.on('end', function() {
    // Decrement the counter, counter will eq 0

Meter: Average calculated values

Things that are measured as events / intervals.

var probe = pmx.probe();

var meter = probe.meter({
  name      : 'req/sec',
  samples   : 1,
  timeframe : 60

http.createServer(function(req, res) {


Sample option is the rate unit. Defaults to 1 sec. timeframe option is the timeframe over which events will be analyzed. Defaults to 60 sec.


Stores a resevoir of statistically relevant values biased towards the last 5 minutes to explore their distribution.

var probe = pmx.probe();

var histogram = probe.histogram({
  name        : 'latency',
  measurement : 'mean'

var latency = 0;

setInterval(function() {
  latency = Math.round(Math.random() * 100);
}, 100);

Common Custom Metrics options

  • name : The probe name as it will be displayed on the Keymetrics dashboard.
  • agg_type : This parameter is optional, it can be sum, max, min, avg (default) or none. It will impact the way the probe data are aggregated within the Keymetrics backend. Use none if this is irrelevant (eg: constant or string value).
  • alert : For Meter and Counter probes. This parameter is optional. It will create an alert object (see below).

Alert System for Custom Metrics

This alert system can monitor a Probe value and launch an exception when hitting a particular value.

Example for a cpu_usage var:

var metric = probe.metric({
  name  : 'CPU usage',
  value : function() {
    return cpu_usage;
  alert : {
    mode  : 'threshold',
    value : 95,
    msg   : 'Detected over 95% CPU usage', // optional
    action: function() { //optional
      console.error('Detected over 95% CPU usage');
    cmp   : function(value, threshold) { //optional
      return (parseFloat(value) > threshold); // default check


  • mode : threshold, threshold-avg, smart.
  • value : Value that will be used for the exception check.
  • msg : String used for the exception.
  • action : optional. Function triggered when the exception level is reached.
  • cmp : optional. Function used for exception check that takes 2 arguments.
  • interval : optional, threshold-avg mode. Sample length for monitored value (180 seconds default).
  • timeout : optional, threshold-avg mode. Time after which mean comparison starts (30 000 milliseconds default).

Report Alerts: Errors / Uncaught Exceptions

Once PM2 is linked to Keymetrics, you will be alerted of any uncaught exception by default. These errors are accessible in Keymetrics Issue page.

Custom alert notification

If you need to alert about any critical errors you can do it programmatically:

var pmx = require('pmx');

pmx.notify({ success : false });

pmx.notify('This is an error');

pmx.notify(new Error('This is an error'));

Add Verbosity to an Alert: Express Error handler

When an uncaught exception is happening you can track the routes from which it has been thrown. To do that you have to attach the middleware pmx.expressErrorHandler at then end of your routes mounting:

var pmx = require('pmx');

// All my routes
app.get('/' ...);;
// All my routes

// Here I attach the middleware to get more verbosity on exception thrown

Emit Events

Emit events and get historical and statistics. This is available in the Keymetrics Events page.

var pmx = require('pmx');

pmx.emit('user:register', {
  user : 'Alex registered',
  email : ''

Application level network traffic monitoring / Display used ports

You can monitor the network usage of a specific application by adding the option network: true when initializing PMX. If you enable the flag ports: true when you init pmx it will show which ports your application is listening on.

You can find these metrics in the Custom Metrics section located in the Keymetrics Dashboard page.


  network : true, // Allows application level network monitoring
  ports   : true  // Displays ports used by the application

HTTP latency analysis

This feature enables you to monitor routes, latency and codes while being REST compliant.

pmx.http(); // You must do this BEFORE any require('http')

You can also ignore some routes by passing a list of regular expressions.

  http          : true, // (Default: true)
  ignore_routes : [/socket\.io/, /notFound/] // Ignore http routes with this pattern (Default: [])

This can alternatively be done via pmx.init().

  http          : true, // (Default: true)
  ignore_routes : [/socket\.io/, /notFound/] // Ignore http routes with this pattern (Default: [])


Massachusetts Institute of Technology: MIT